Plastocyanin (PC) is a 10.5 kD blue copper protein which functions in chloroplast electron transfer. A chemical modification approach will be used to study binding sites, conformational changes and electrostatic effects in PC. A series of carboxyl modified PC's has been prepared which contains molecules of ethylenediamine at specific locations. A series of amino modified PC's will also be prepared. These will be used to study the interaction of PC with its physiological reaction partners (cytochrome f and P700) in order to determine where they bind on the PC molecule. The effect of modification on the reactions of PC with negatively and positively charged artificial electron donors and acceptors will be studied in order to determine the effect of changing the charge on PC at one location on reactions occurring at another. Effects on the midpoint redox potential and its pH dependence will also be determined. NearUV CD and flourescence will be used to determine whether modification causes conformational changes in PC. NMR will be used to determine whether modification affects thee ligands to the copper in reduced PC. A cyt f PC adduct (Davis and Hough, 1983) will be made in order to determine whether adduct formation alters the redox potential of PC. The results of this study will increase our knowledge of electron transport mechanisms.